Convertible furniture has been in use for many years and has served well to provide additional sleeping accommodations for both regular and occasional use. The furniture may be an elongate sofa or a suitable chair and both will be included in the term "sofa" or "sofa bed" as used hereinafter. Most of such furniture now on the market is in the form of an elongate sofa bed having loose seat cushions which may be removed and set aside to expose an articulated bed frame assembly folded in compact arrangement and stored within a cavity in the rigid stationary frame of the sofa. One section of the assembly is pivotally connected to the stationary frame on a transverse axis, and the section which is uppermost in storage position may be grasped and manually raised and pulled outwardly. All of the sections are pivotally connected to each other to be unfolded successively as the extension movement proceeds, to form a substantially horizontal bed frame with supporting legs extending down beneath the outer portions.
The manual operations involved in extending and retracting the frame have proven to be both difficult and laborious. The sections are large and the operator must bend far forward to grip them. In addition they are rather heavy, so that the elderly and infirm are hard pressed to manipulate them. Many efforts have been made to overcome the difficulties by applying a power drive to the system of links and levers, and they have succeeded in eliminating the burden on the operator. However, the known power drive systems suffer from one or more drawbacks. One of the most serious is that they unfold and extend the sections in separate independent steps. using pin and slot sliding connections, cams, and limit stops to complete one swinging motion and commence the next. The result is a loose-jointed assembly which tends to misalign, bind, and stick while making a substantial amount of noise. None of them has a really positive system for maintaining accurate alignment of the transversely spaced sets of linkages to prevent binding. And none of them is so constructed that it can be operated manually in the event of power failure without disconnection or adjustment of some of the operating parts.
The patent to Willis, U.S. Pat. No. 2,934,770, dated May 3, 1960, discloses a worm/nut drive at each side of an articulated bed frame assembly operated by an electric motor to extend or retract the frame assembly. Push bars actuated by the worm/nut drives extend and retract the frame sections. The linkage includes pin and slot connections, cams, and limit stops to produce independent, discontinuous movements of the frame sections. The push bars have to be disconnected to permit manual operation of the assembly.
The patent to Thomas, U.S. Pat. No. 2,972,753, dated Feb. 28, 1961, discloses a drive linkage for extending and retracting the frame assembly actuated by a rack and pinion drive operated by an electric motor. The motor is at one side of the bed, and the long torque shaft extending to the drive at the other side is subject to torsional twisting which can cause misalignment between the two drives. There is no cable drive and there is no provision for mattress storage.
The patent to Heisler, U.S. Pat. No. 3,080,574, dated Mar. 12, 1963, discloses a manually extended and retracted frame assembly having one frame section slidable over the other and a cable loop to maintain alignment. There is no power drive and no practical way to apply one.
The patent to Katz, U.S. Pat. No. 3,281,871, dated Nov. 1, 1966 discloses diamond shaped throw-out links pivotally anchored to the stationary frame. The linkage is manually actuated and folds and unfolds in step by step sequence.
The patent to Usievich, U.S. Pat. No. 1,260,600, dated Mar. 26, 1918, discloses a three section frame assembly, pivotally carried by a pair of triangular links pivotally connected to the stationary frame. There is no power drive, and the assembly is folded and unfolded manually in a step by step operation.